This invention relates to a bismuth containing, corrosion resistant copper-nickel-manganese-zinc alloy suited for use in food handling machinery. This anti-galling alloy may be statically or continuously cast into different shapes and forms.
Traditionally "Dairy Metals" have been used in many food processing parts. Dairy metals are copper-nickel alloys containing varying amounts of tin, zinc, and lead. Lead has been an essential ingredient for these alloys because their anti-galling properties depend on it. Lead also improves machinability of these alloys. Typically, lead content of Dairy Metals lies between 2 and 7 percent by weight.
Toxicity of lead is now well established. Ingestion of even a few parts per million of lead into the human body causes significant concern with the medical community. As a consequence, special efforts have been made to eliminate lead from materials which might end up in human body. Lead has been generally replaced by bismuth in many anti-galling and low friction alloys. The same is true for alloys requiring good machinability. Examples of bismuth-bearing nickel-base anti-galling alloys are those of Thomas and Williams (U.S. Pat. No. 2,743,176) and of Larson (U.S. Pat. No. 4,702,887). These alloys have been in use for decades. However these alloys are very expensive and are restricted to only special applications.
More recently, bismuth has been used to replace lead in dairy metals (Sahu; U.S. Pat. No. 5,242,657). This alloy has good corrosion and anti-galling characteristics but suffers from low strength and very poor ductility. As a result, very thin parts like scraper blades made out of this alloy fracture during use or shatters if mishandled during finishing process. Because of low strength of alloy of U.S. Pat. No. 5,242,657; food forming plates can not be made thinner than about 0.3 inches because they fracture during use. Low ductility of this alloy sometimes leads to fracture during straightening of machined parts.
Therefore, the objectives of this invention are the following:
1. A moderate cost alloy PA1 2. Alloy with good corrosion and anti-galling properties PA1 3. Alloy with strength and ductility substantially higher than those of U.S. Pat. No. 5,242,657 PA1 Tensile Strength=42-58 KSI PA1 Yield Strength=34-45 KSI PA1 Percent Elongation=3-8 PA1 Hardness=110-175 BLN